There have heretofore been known TN type liquid crystal display devices having a TN (twisted nematic) type liquid crystal cell which comprises two substrates each having, on the surface, a liquid crystal alignment film via a transparent electroconductive film and a nematic liquid crystal layer having a positive dielectric anisotropy, the nematic liquid crystal layer being interposed between the two substrates so as to form a sandwich structure, in which liquid crystal cell the major axes of liquid crystal molecules are continuously twisted by 90.degree. in the direction extending from one of the substrates to the other substrate. The alignment of liquid crystal in the TN type liquid crystal devices is made generally by a liquid crystal alignment film imparted with an alignability for liquid crystal molecules by a rubbing treatment. As the material for the liquid crystal alignment film, there are hitherto known resins such as polyimide, polyamide, polyester and the like. Polyimides, in particular, are used in many liquid crystal display devices because of the excellency in heat resistance, compatibility with liquid crystal, mechanical strengths, etc.
When a TN type liquid crystal display device is produced using a liquid crystal alignment film formed of conventionally used polyimide or the like, however, the liquid crystal display device has problems in that it gives defective display due to its low pretilt angle or an image sticking is caused owing to its a large residual voltage. Hence, it has been desired to develop a liquid crystal alignment agent capable of giving a liquid crystal display device which has a liquid crystal alignment film of good liquid crystal alignability and a high pretilt angle and is excellent in low image retention properties.